FLOOD RISK and EARLY WARNING SYSTEMS About IHCAP
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SCIENCE BRIEF: FLOOD RISK AND EARLY WARNING SYSTEMS About IHCAP The Indian Himalayas Climate Adaptation Programme (IHCAP) is a project under the Global Programme Climate Change and Environment (GPCCE) of the Swiss Agency for Development and Cooperation (SDC), and is being implemented in partnership with the Department of Science and Technology (DST), Government of India. IHCAP is supporting the implementation of the National Mission for Sustaining the Himalayan Ecosystem (NMSHE) as a knowledge and technical partner. The overall goal of IHCAP is to strengthen the resilience of vulnerable communities in the Himalayas and to enhance and connect the knowledge and capacities of research institutions, communities and decision-makers. Published by IHCAP Authors: Juan Antonio Ballesteros Canovas, Divya Mohan, Markus Stoffel, Mustafa Ali Khan, Janine Kuriger, Shirish Sinha Copyediting: Shimpy Khurana Photo Credits: Prashanth Vishwanathan/IHCAP Copyright © IHCAP 2017. All Rights Reserved. Published in India This science brief or parts of it may not be reproduced, stored by means of any system or transmitted, in any form or by any medium, whether electronic, mechanical, photocopied, recorded or of any other type, without the prior permission of IHCAP. This science brief is available in the electronic form at: http://www.ihcap.in/resources.html SCIENCE BRIEF: FLOOD RISK AND EARLY WARNING SYSTEMS INTRODUCTION In Himachal Pradesh (HP), floods are the most frequent and prevalent natural disaster caused due to intense rainfalls during the monsoon season. Demographic pressure coupled with development of human settlements and infrastructure in the most exposed locations further aggravates the problem. Each year, extreme floods occur in mountain catchments upstream causing economic losses as well as fatalities in the inhabited valleys downstream. The causes of flood disasters in HP include (i) long-duration monsoon rainfall (ii) cloudburst phenomena due to localized, intense downpours (iii) glacier lake outburst floods (GLOFs) caused by the sudden outburst of glacier lakes1 and/or (iv) landslide lake outburst floods (LLOFs) caused by the outburst of lakes formed by landslides. Flash floods (especially from cloudbursts) and monsoon floods are the most common processes, and hence, the focus of this science brief. Since the mid-20th century, more than 5,000 casualties have been reported as a result of floods in HP. The recorded flood events point to Kullu district as the most affected area in the state (Randhawa et al., 2016). Most of the inhabited valleys in the Indian Himalayan Region (IHR) have high risk of floods (Ballesteros-Canovas et al., 2017). The situation is unlikely to improve, and more such events could be expected over the next decades due to developmental pressure, related land-use changes (in terms of urbanization and tourism), and impacts of climate change and extreme events. These circumstances call for suitable adaptation measures and related policies based on robust scientific assessments. However, the main challenge in IHR is the lack of historical flow records and high-quality data on past floods. This prevents the development of long-term, high-quality predictions of future flood trends. This science brief focusses on the main results from the research conducted under the Indian Himalayas Climate Adaptation Programme (IHCAP), a project of the Swiss Agency for Development and Cooperation (SDC) on flood processes. The aim of the research was to develop innovative and sustainable approaches for regional flood risk assessments and adaptation planning in Kullu district. The technical results from the research have been simplified and presented in a comprehensive manner to deliver key messages for policymakers. This document presents: (1) a summary of the frequency of flood events in Kullu district (2) an analysis of elements-at-flood risk used as a basis for flood hazard zonation 1A lake outburst can be triggered by several factors such as ice or rock avalanches, the collapse of the moraine dams due to the melting of ice buried within, earthquakes or sudden inputs of water into the lake e.g. through heavy rains or drainage from lakes further up the glacier. GLOFs lead to sudden release of large volumes of water in very short interval of time resulting in flooding in the downstream areas. 1 1 Floods in Kullu district (i.e. Beas, Parvati, Sainj and Tirthan Rivers) have FREQUENCY OF taken place repeatedly (Figure 1) with at least 66 floods since 1965, FLOOD DISASTERS defining an average frequency of 1.1 events per year (Ballesteros-Canovas et al., 2017). This average flood frequency is based on the existing flow IN KULLU DISTRICT discharge records and on the paleoflood reconstruction2 using tree-rings3. The analysis was carried out at six different river reaches in the catchments of Upper Beas, Lower Parvati River, Tirthan River at up and downstream Gushaini; and Sainj River upstream Telara Dam (Figure 2, Labels 1-6). In most cases, reconstructed events in the recent five decades have matched with those recorded downstream by flow gauges. Overall, as per the flow gauge records, 17 flooded years have been observed since 1956, whereas tree-rings have provided evidence of 22 past flooding events since 1910. The comparison between both records suggests that > 40 percent of the reconstructed events were recorded by the flow records during last decades. Yet, the 60 percent of events were not previously observed, and therefore indicate the add value of the gathered flood reconstruction. 2Paleofloods reconstruction refers to floods previously not recorded and such reconstruction of the magnitude and frequency of recent, past, or ancient floods is done using geological evidence (Baker, 2008; Kochel and Baker, 1982). 3Peak discharge reconstruction based on tree-rings is a Embankment of the Beas River at the main Kullu-Manali road destroyed during the scientific approach of estimating the flow discharge Figure 1 2005 flood event. Source: http://hillpost.in/2014/07/muck-dumping-a-threat-to-beas based on indicators such as the height of scars on trees -river-valley/99667/ caused during past floods (Ballesteros-Cánovas et al., 2015). 2 The occurrence of floods is not expected to decrease, and its consequences could become even worse in view of the ongoing climatic changes and increasing demographic pressure. Data indicates that the flood season in Kullu district normally lasts from June to September, with peaks in flood activity in July and August. The intensity of floods is the highest in the Upper Beas River (above Manali) (Figure 2, Label 1) and Sainj River (down to Telara Dam) (Figure 2, Label 2). The streamflow extremes observed in Sainj River (at Larji) (Figure 2, Label 3) was comparatively lower probably due to flow regulation by existing dams (Ballesteros-Canovas et al., 2017). The flood assessment for Kullu indicates variation in hazard levels for different catchments located in the district suggesting the need for local-level assessments in order to identify adaptation measures. 77o0’0”E 77o20’0”E 77o40’0”E Villages Flow gauge 20’0”N o 20’0”N o Analysed site 32 32 1 MANALI PARVATI RIVER 0’0”N o 0’0”N KASOL o 32 BEAS RIVER 32 2 BHUNTAR 3 SAINJ RIVER TIRTHAN RIVER 4 40’0”N 5 o 40’0”N o N 31 31 6 0 4 8 16 24 32 Km 77o0’0”E 77o20’0”E 77o40’0”E Map of Kullu district showing the studied catchment (border in red), the location of the available gauge stations Figure 2 (black dots with a cross) and all the paleoflood studied sites where reconstruction of ungauged flood events were conducted (Labels 1-6). The location of the examples related to man-made flood disaster sites correspond to the Labels: 1, 4 and 5 (See Box 1). Source: Juan Antonio Ballesteros Cánovas. 3 EXAMPLES OF MAN-MADE FLOOD DISASTERS IN KULLU DISTRICT BOX 1 Human activities in the floodplains have sometimes been the cause of flood disasters in Kullu district. A) Human activities near a river channel can cause flood disaster. This is indicated by the example of construction at Palchan village on the banks of Beas River (Figure 2, Label 1). At this site, the construction of a new bridge connecting Palchan with Solang resulted in major modifications in the river channel. As a consequence, during the moderate flood of July 2012, the local school, the hydropower plant as well as bridges located further downstream were seriously damaged (Figure 3a). B) Lack of hazard zonation enhances future flood risk for infrastructure. During the flood of July 2005, a combination of flood in the main Tirthan River and an intense debris flow in a nearby tributary system resulted in major changes in the river channel upstream of Gushaini village (Figure 2, Label 4). Large amounts of sediment (with boulders up to 2 m in diameter) came downstream and changed partially the river corridor at Gushaini village, where severe damage was reported. Despite the occurrence of this major event, a new school and other infrastructure have been constructed in the now-abandoned channel (Figure 3b). C) Lack of risk perception and land management will result in future disasters. This is indicated by the example of construction work at an elevated section of Tirthan River formed due to deposition of sediments, ca. 10 km downstream of Gushaini village (Figure 2, Label 5). The section was significantly flooded during July 2005. Despite the flood disaster, massive construction work for tourist facilities started within this section in 2006 (Figure 3c). 4 Figure 3 Figure 3a Severe damage at the primary school located at Palchan village after the 2012 flood in Beas River. Figure 3b School constructed in the abandoned channel of Tirthan River upstream of Gushaini village after the flood in 2005. Figure 3c Tourist facility constructed at a section of Tirthan River after it was flooded in 2005.